The present techniques relate generally to bit-wise optical data storage techniques. More specifically, the techniques relate to methods and systems for decoding data from optical storage systems.
As computing power has advanced, computing technology has entered new application areas, such as consumer video, data archiving, document storage, imaging, and movie production, among others. These applications have provided a continuing push to develop data storage techniques that have increased storage capacity. Further, increases in storage capacity have both enabled and promoted the development of technologies that have gone far beyond the initial expectations of the developers, such as gaming, among others.
The progressively higher storage capacities for optical storage systems provide a good example of the developments in data storage technologies. The compact disc, or CD, format, developed in the early 1980s, has a capacity of around 650-700 MB of data, or around 74-80 min. of a two channel audio program. In comparison, the digital versatile disc (DVD) format, developed in the early 1990s, has a capacity of around 4.7 GB (single layer) or 8.5 GB (dual layer). The higher storage capacity of the DVD is sufficient to store full-length feature films at older video resolutions (for example, PAL at about 720 (h)×576 (v) pixels, or NTSC at about 720 (h)×480 (v) pixels).
However, as higher resolution video formats, such as high-definition television (HDTV) (at about 1920 (h)×1080 (v) pixels for 1080p), have become popular, storage formats capable of holding full-length feature films recorded at these resolutions have become desirable. This has prompted the development of high-capacity recording formats, such as the Blu-ray Disk™ format, which is capable of holding about 25 GB in a single-layer disc, or 50 GB in a dual-layer disc. As resolution of video displays, and other technologies, continue to develop, storage media with ever-higher capacities will become more important.
One developing storage technology that may better achieve future capacity requirements in the storage industry is based on holographic storage. Holographic storage is the storage of data in the form of holograms, which are images of three dimensional interference patterns created by the intersection of two beams of light in a photosensitive storage medium. In bit-wise holography or micro-holographic data storage, every bit may be written as a micro-hologram, or Bragg reflection grating, typically generated by two counter-propagating focused recording beams. The writing process may also involve encoding the data. For example, error correcting codes or modulation codes may be used to encode the data as it is stored in an optical disc. The data is then retrieved by using a read beam to reflect off the micro-hologram to reconstruct the recording beam, and typically involves decoding the data to retrieve the information originally stored.
Although holographic storage systems may provide much higher storage capacities than prior optical systems, as is the case for all optical storage media, they may be vulnerable to interferences. For example, interferences may result from the closely spaced bits in adjacent tracks and layers, or electronic interferences produced by the optical storage system. Decoding techniques which reduce the errors resulting from optical and electronic noise may be advantageous.